The present invention relates generally to a sheet or envelope feeder and, more specifically, to the feeding mechanism of a feeder.
Sheet and envelope feeders are commonly used in an envelope insertion system where envelopes are fed, one at a time, into an envelope inserting station, and enclosure documents are released into a gathering device for collation before the enclosure documents are inserted into the envelope at the envelope inserting station. They are also used in many different types of printers, photo copiers, print presses, and so forth. In those feeders, the most commonly used feeding mechanism is a drive roller assembly having a plurality of rollers mounted on a common shaft to be driven by a motor for rotation.
A typical envelope printer 100 is shown in FIG. 1. As shown, the printer 100 has a rack 102 for supporting a stack of envelopes 104 to be fed into the printing area 106. The feeding mechanism of the printer 100 comprises a set of six (6) drive rollers 108 for moving the envelopes 104, one at a time, into the printing area 106. On top of each drive roller 108 is a separator 110 forming a separation gap 112 to admit one (1) envelope 104 at a time into the printing area 106. The separation gap 112 is adjustable according to the thickness of the envelope 104.
In a prior art drive roller assembly 120, as shown in FIG. 2, the drive rollers 108 are fixedly mounted on a drive shaft 114. The drive shaft 114 is operatively connected to a motor 116 for rotation. A torque limiting device 118 is mounted between the motor 116 and the drive shaft 114 to set a maximum torque such that when the tangential force 122 exerted on the periphery 124 of one or more of the rollers 108 exceeds the maximum torque, all the rollers 108, along with the drive shaft 114, are mechanically decoupled from the motor 116. In order to accommodate envelopes having certain ranges of thickness, the maximum torque for a feeding mechanism in a printer is set to usually about 10 pounds. Accordingly, when the motor 116 is turning, the rollers 108 are stopped only when the tangential force 122 exceeds ten (10) pounds. If an operator accidentally inserts a finger into one of the separation gaps 112, this would result in discomfort or even injury to the operator. In order to reduce this safety hazard, it would be necessary to substantially reduce the maximum torque. However, with the driving assembly 120 as shown, it would be impractical to reduce the maximum torque far beyond the ten (10) pound limit for this would adversely affect the feeding function of the feeding mechanism.
It is, therefore, desirable to provide a method and a device for reducing the maximum torque of the driving rollers without adversely affecting the feeding function of the drive roller assembly while greatly reducing the safety hazard to the operator.
The present invention provides a method and a device for reducing the maximum torque to the rollers in a feeder for feeding substantially flat items such as printed documents, envelopes, cardboards and so forth. While the maximum torque to the individual rollers of the feeder is substantially reduced so as to greatly reduce the safety hazard to the operator, the feeding function of the feeder is not adversely affected. The device for reducing maximum torque, according to the present invention, comprises a drive roller assembly which includes: a drive shaft having a longitudinal axis operatively connected to a driving device for rotation about the longitudinal axis; a plurality of rollers mounted on the drive shaft for motion; and a plurality of torque limiting devices, each separately engaged with a roller for mechanically coupling the roller to the drive shaft and setting a maximum torque to the roller so that the roller is driven along with the drive shaft when a tangential force exerted on the roller does not exceed the maximum torque and the roller is mechanically decoupled from the drive shaft when the tangential force exerted on the roller exceeds the maximum torque, while such decoupling is accomplished without affecting the motion of the other rollers.
Accordingly, the method for reducing the torque to the drive rollers mounted on a common drive shaft in a drive roller assembly, according to the present invention, comprises the step of engaging a separate torque limiting device to each roller for mechanically coupling the roller to the drive shaft and setting a maximum torque to the roller so that the roller is driven along with the drive shaft when the tangential force exerted on the roller does not exceed the maximum torque and the roller is mechanically decoupled from the drive shaft when the tangential force exerted on the roller exceeds the maximum torque. Because each roller has a separate torque limiting device for setting the maximum torque, a roller can be mechanically decoupled from the drive shaft without adversely affecting the motion of the other rollers.
In other words, the method and device for reducing the torque to the drive rollers mounted on a common drive shaft in a drive roller assembly, according to the present invention, replaces a single torque limiting device for the entire drive roller assembly with a plurality of torque limiting devices, one for each roller. With each roller having a separate torque limiting device, the rollers will share the torque required for the entire feeding mechanism to function properly. Therefore, the maximum torque set for each of the rollers is only a fraction of the maximum torque when a single torque limiting device is used for the entire drive roller assembly.
The method and device, according to the present invention, will become apparent upon reading the description taken in conjunction with FIG. 3 to FIG. 8.